The field of invention relates generally to communication; and more specifically, to a method and apparatus for an egress channel architecture that supports protection within SONET/SDH based networks.
Synchronous Optical NETwork (SONET) and Synchronous Digital Hierarchy (SDH) based networks typically emphasize redundancy. That is for example, should a particular network line that couples a pair of nodes within the network fail (or degrade), the network is designed to xe2x80x9cswitch overxe2x80x9d to another network line so that traffic flow is not substantially interrupted. Various types of redundancy may be designed into a SONET network. Some examples are illustrated in the discussion that follows.
FIG. 1 shows a point-to-point perspective. Point to point redundancy focuses on the behavior of a pair of nodes 131, 132 that are coupled together by a plurality of SONET lines 1041, 1042, . . . 104xxe2x88x921, 104x. Although other point-to-point schemes may be possible, common point-to-point schemes typically include 1+1 and 1:N. Both schemes classify a network line as either a working line or a protection line. A working line is deemed as the xe2x80x9cactivexe2x80x9d line that carries the information transported by the network. A protection line serves as a xe2x80x9cback-upxe2x80x9d for a working line. That is, if a working line fails (or degrades), the protection line is used to carry the working line""s traffic.
In a 1+1 scheme, both the working and protection lines simultaneously carry the same traffic. For example, referring to FIG. 1, if line 1041 is the working line and line 1042 is the protection line; the transmitting node 131 simultaneously transmits the same information on both the working line 1041 and the protection line 1042. The receiving node 132, during normal operation, xe2x80x9clooks toxe2x80x9d the working line 1041 for incoming traffic and ignores the incoming traffic on the protection line 1042. If a failure or degradation of the working line 1041 is detected, the receiving node 132 simply xe2x80x9clooks toxe2x80x9d the protection line 1042 for the incoming traffic (rather than the working line 1041).
In a 1:N scheme one protection line backs up N working lines (where N is an integer greater than or equal to 1). For example, referring to FIG. 1, lines 1041 through 104xxe2x88x921 may be established as the working lines while line 104x may be established as the protection line. If any of the working lines 1041 through 104xxe2x88x921 fail or degrade, the transmitting node 132 sends the traffic of the failed/degraded working line over the protection line 104x. The receiving node 132 also xe2x80x9clooks toxe2x80x9d the protection line 104x for the traffic that would have been sent over the failed/degraded working line prior to its failure/degradation.
FIG. 2 shows a ring perspective. Ring redundancy schemes focus on the behavior of a plurality of nodes 231 through 234 coupled together in a ring. Redundancy is handled by sending identical streams of traffic in opposite directions. A first direction may be referred to as the working direction while a second direction may be referred to as the protection direction. In a Unidirectional Line Switched Ring (ULSR) approach, working traffic is sent in a first direction around the ring (e.g., clockwise) and protection traffic is sent in a second direction around the ring (e.g., counter-clockwise).
In a Bi-directional Path Switched Ring (BPSR), the working traffic flows in the xe2x80x9cfastestxe2x80x9d direction. That is, of the two directions around the ring from a transmitting node to a receiving node, a first direction will have a shorter propagation delay than a second direction. For each transmitting/receiving node pair, the working traffic corresponds to the direction having the shorter propagation delay and the protection traffic corresponds to the direction having the longer propagation delay. In either the ULSR or BPSR approaches, if failure or degradation occurs in the working direction, active traffic is looked for in the protection direction.
More sophisticated SONET networks may also be designed that provide protection at higher degrees of resolution. That is, each SONET line (such as line 1041 of FIG. 1 or line 204 of FIG. 2) may be viewed as transporting a number of STS-1 signals. For example, if lines 1041 and 204 each correspond to an STS-n line, each of these lines may be viewed as carrying n STS-1 signals (e.g., an STS-48 line may be viewed as carrying 48 STS-1 signals).
Furthermore, in other environments, each STS-1 signal is used as a resource for carrying a plurality of lower speed signals. Protection may be provided for STS-1 signals individually or for their constituent lower speed signals individually. Either of these forms of protection are commonly referred to as xe2x80x9cpath protection. For example, in one type of 1+1 path protection scheme, an individual xe2x80x9cworkingxe2x80x9d STS-1 signal within an STS-n line (rather than all the STS-1 signals on the STS-n line) is backed up by a xe2x80x9cprotectionxe2x80x9d STS-1 signal transported on another STS-n line.
Automatic Protection Switching (APS) is a protocol that may be executed by the nodes within a SONET network. APS allows SONET nodes to communicate and organize the switching over from their working configuration to a protection configuration in light of a failure or degradation event. For example, in a typical approach, K1 and K2 bytes are embedded within the SONET frame that is communicated between a pair of nodes in order to communicate failure/degradation events, requests for a switch over, etc.
FIG. 3 shows a distributed xe2x80x9cfull meshxe2x80x9d switch architecture 331. The architecture 331 of FIG. 3 may be utilized to implement a SONET node such as nodes 131, 132 of FIG. 1 or nodes 231 through 234 of FIG. 2. An ingress channel receives incoming data from a networking line. FIG. 3 shows ingress channels 3011 through 301x that each receive incoming data on a respective network line 3031 through 303x.
An egress channel transmits outgoing data onto a networking line. FIG. 3 shows egress channels 3121 through 312x that each transmit outgoing data on a respective network line 3041 through 304x. In a full mesh architecture, each ingress channel 3011 through 301x transmits all of its ingress traffic to each egress channel 3121 through 312x. For example, referring to FIG. 3, ingress channel 3011 receives n STS-1 signals from its corresponding network line 3031 (e.g., if network line 3031 is an OC-48 line; n=48 and the ingress line channel receives 48 STS-1 signals).
All n of the STS-1 signals received by the ingress channel 3011 are transmitted across the node""s backplane 305 over each of its output lines 306, 310, 311, 312. As a result, each egress channel 3121 through 312x receives all n STS-1 signals received by ingress channel 3031. In one approach, each STS-1 signal is provided its own signal line to each egress channel. As a result, each output 306, 310, 311, 312 corresponds to a n-wide bus.
As each ingress channel is similarly designed, each egress channel 3121 through 312x receives all the incoming traffic received by the node. For example, in the particular example of FIG. 3, there are x ingress channels 3011 through 301x that each receive n STS-1 signal. As such, each egress channel 3121 through 312x receives xn STS-1 signals (which correspond to the total amount of traffic received by the node 331).
For example, note that egress channel 3121 receives inputs 306 through 309 where each of these inputs correspond to the n STS-1 signals received by their corresponding ingress channel (i.e., input 306 for ingress channel 3011, input 307 for ingress channel 3012, input 308 for ingress channel 3013, . . . and input 309 for ingress channel 301x). In order to implement the switching fabric of the node, each egress channel 3121 through 312x is configured to select n of the xn STS-1 signals and transmit the n STS-1 signals over its corresponding outgoing networking line 3041 through 304x.